Generally, a so-called dual injection type internal combustion engine is known which includes an injector for in-cylinder injection which injects fuel into a cylinder and an injector for intake passage injection which injects fuel into an intake passage or an intake port and switches between them for use depending on the operational state of the engine to realize, for example, stratified charge combustion in a low-load operational region and homogeneous charge combustion in an intermediate/high-load operational region such that the ratio of fuel injections from both injectors is appropriately changed in accordance with the operational state in the homogeneous charge combustion region. For example, see Patent Document 1.
In addition, Patent Document 2, for example, describes a technique in which when ignition timing is corrected for retard in order to prevent knocking produced in transition such as during acceleration, that is, transitional knocking, the retard correction of the ignition timing is performed by taking account of influences of the temperature of cooling water or the temperature of intake air.
In the technique described in Patent Document 2 mentioned above, the retard correction of the ignition timing is performed in consideration of influences of the cooling water temperature or the intake air temperature, and this is effective for an engine which includes only an injector for intake passage injection. However, this technique is not effective if it is applied without any change to a dual injection type internal combustion engine which includes an injector for in-cylinder injection and an injector for intake passage injection such that the ratio of fuel injections from both injectors is changed depending on the operational state. This is because a change in the ratio of fuel injections from the injector for in-cylinder injection and the injector for intake passage injection leads to a change of the temperature of intake air in the cylinder, that is, the in-cylinder intake air temperature to change the conditions under which the transitional knocking occurs, thereby presenting problems such as poor acceleration due to the overcorrection for retard and the occurrence of knocking due to undercorrection for retard.
(Patent Document 1) Japanese Patent Application Laid-Open No. 2001-20837
(Patent Document 2) Japanese Patent Application Laid-Open No. 7-180643 (1995)